The present invention relates to a semiconductor device, a method of fabrication thereof and an applied circuit thereof, or more in particular to an overvoltage self-protection semiconductor device, a method of fabrication thereof and a semiconductor circuit using such a circuit capable of self-protection of a semiconductor device against an overvoltage, which turns on safely even upon application thereto of an overvoltage exceeding a breakdown voltage of the semiconductor device.
A prior art example relating to a semiconductor device having the self-protection function against an overvoltage is disclosed in JP-A-59-172771.
According to this conventional device, a thyristor has a voltage breakdown region at a portion thereof where the forward blocking voltage is lower than that in the remaining regions. Specifically, a part of the p-base layer of a thyristor is etched into a well form, and diffused with p-type impurities to form a p-type base layer. The electric field is concentrated in the curved area of a newly-formed p-base layer, thus causing an avalanche breakdown. A pilot thyristor is turned on by the prevailing current as a trigger.
Also, the prior art described in JP-A-59-158560 discloses another conventional semiconductor device having the self-protection function against an overvoltage.
According to this conventional device, a light triggered thyristor has a recess at a part of the p-base region thereof, and a partial thyristor is formed with a thinner n-base, so that when a forward voltage is applied, the pnp portion of the partial thyristor is punched through, thereby providing self-protection against an overvoltage.